The present invention concerns aqueous hydraulic cement slurry compositions.
Hydraulic cements, i.e., any inorganic cement that hardens or sets under water, are customarily admixed with water and emplaced as aqueous slurries. The amount of water employed may vary rather extensively dependently largely upon the fluidity of the slurry required and upon the necessary ultimate strength. In a great many uses of a hydraulic cement it is necessary for the cement slurry to be emplaced within or next to a porous medium, for example, earthen strata, e.g., in the cementing off of boreholes, grouting, dam and tunnel construction and the like. When such is the case water filters out of the slurry and into the strata during the setting period. When this occurs to any appreciable extent there usually results an uncontrolled setting rate, improper placement, impaired strength properties and usually a contamination of the surrounding strata. All of these undesirable conditions are especially to be avoided in cementing operations associated with oil, gas, water or brine wells. In an effort to lessen the loss of fluid from an aqueous hydraulic cement slurry various materials have been employed. One such material comprises a polyamine compound selected from the class consisting of polyalkylenimines, polyalkylenepolyamines and mixtures thereof. A description of these polyamine compounds and their use in hydraulic cement slurries is taught, for example, in U.S. Pat. No. 3,491,049, the teachings of which are specifically incorporated herein by reference. Although these polyamino compounds are quite satisfactory in environments wherein the temperature of the hydraulic cement slurry does not increase to above about 200.degree. F., the fluid loss characteristics of these cement slurries are unacceptable at higher temperatures.
U.S. Pat. No. 4,131,578 discloses fluid loss additive compositions suitable for use at temperatures of 200.degree. F. and above.
The present invention provides for fluid loss additives which are more efficient, i.e. they require less active additive to achieve the same level of water loss or at the same level of active additive less water loss occurs while also providing more stable, non-settling, cement slurries.